A liquid crystal display device includes a light control unit (liquid crystal panel) that can change the transmission state of light and also includes a light source (back light) that emits light toward the back surface of the light control unit. A liquid crystal display device turns on the light source and controls the transmittance of light irradiating the light control unit in accordance with the content of an image to be displayed so that a given image is displayed.
If an image to be displayed contains a black part, a liquid crystal display device sets the transmittance of light irradiating the black part to the lowest possible level; however, a light control unit does not block the amount of light emitted from the light source entirely. Therefore, a liquid crystal display device does not decrease the luminance of a black part to a value sufficiently low level and the contrast of a displayed image is decreased. Moreover, because a back light always irradiates with a luminance maintained at the same level, a large amount of power is consumed lighting the back light.
A technology that prevents a decrease in the contrast involves arranging multiple light sources on the back surface of a light control unit in a grid in such a manner that areas irradiated by their respective light sources are independent from each other and controlling the emission intensity of each of the light sources is in accordance with the image to be displayed (Japanese Laid-open Patent Publication No. 2005-258403 and Japanese Laid-open Patent Publication No. 2006-147573).